I actually think the Big Stik is a pretty good choice for a trainer as long as the throws are set up gently. It has more dihedral than most of the other stiks on the market, so it's self-correcting tendancies are decent. They slow down nicely for landing like a typical trainer. If you fly in a fairly windy part of the country, the Big Stik might be a good choice because it is less likely balloon into a turn than a flat-bottomed wing trainer.

If the rates are set up gentley and the plane is buddy boxed and flown with a decent instructor, a Big Stik should be just fine as a trainer.